This invention relates to photographic apparatus and more particularly, it concerns a ranging and lens focusing module by which an automatic ranging system may be incorporated in an existing camera structure with minimal modification to such existing structure.
U.S. Pat. No. 3,979,762 and No. 4,052,728 issued respectively on Sept. 7, 1976 and on Oct. 4, 1977 to Donald H. Hendry et al., both assigned to the assignee of the present invention, disclose cameras constructed as an assembly of functional modules supported by a primary structural member which defines the camera exposure chamber. The several modules may include, for example, a shutter module, a gear train module, a viewfinder module and a spreader module. Each module represents an independent operating component and as such, may be manufactured independently through to and including pre-testing prior to assembly in the final structure. Each of the modules, moreover, is designed to be assembled to the primary support structure and enclosed within a protective housing completely by complementing snap fastener formations provided as integral module components. As a result, the modules may be assembled without complicated assembly operations to provide highly sophisticated, completely automated and reliable instant cameras which are presently available to the general public at modest costs.
As pointed out in the texts of the afore-mentioned issued patents, a primary manufacturing advantage of the functioning module approach to camera assembly is that technological advances, which represent changes and correspondingly, increased manufacturing costs as a result of such changes alone, can be incorporated without need for additional or modified expensive assembly equipment. In other words, manufacturing costs incident to the addition of an operating function to a basic camera structure is confined largely to the cost of the module providing that function.
While the savings in manufacturing costs resulting from modular construction of components in photographic cameras has been demonstrated in practice and is thus now apparent, it is equally apparent that the incorporation of new technology in a module capable of direct assembly with an existing camera is not attained without substantial innovative and developmental effort. In a commonly assigned co-pending application Ser. No. 729,289, filed Oct. 4, 1976 in the name of Edwin K. Shenk, now abandoned and replaced by application Ser. No. 916,114, filed on June 16, 1978, there is disclosed a camera lens focusing mechanism in which a sonic pulse generated by a camera mounted transducer is reflected from a subject to be photographed and received by the transducer to provide a range signal related to camera-subject distance. An electronic logic circuit responds to the range signal to produce a train of pulses, the number of which is representative of the lens mount axial position at which the subject will be focused. Such pulses are gated into a counter and used for operating a drive motor coupled mechanically to the lens mount. An encoder wheel coupled rotatably with the lens mount operates as a component of an auxiliary pulse generator in a feedback system so that rotation of the drive motor under the control of the counter causes the auxiliary pulse generator to produce a pre-determined number of pulses for each axial unit displacement of the lens mount. The logic circuit further responds to the output of the auxiliary pulse generator to determine when the lens mount has been moved to the position determined by the pulse train counter to be proper for focusing the subject to be photographed. Such further logic circuitry response results in a pawl engaging a lens mount rack to stop movement of the lens mount at the proper focusing position even though the drive motor may continue to rotate. A slip clutch in the drive train between the motor and the lens mount facilitates this latter operating characteristic.
The state of the art relating to electronic logic circuitry presents no problem to the incorporation of such a system in an existing structure primarily because such circuitry may be embodied physically in a chip or board capable of being positioned in available space within a protective casing of a camera, for example. The requirements of a mechanical system capable of reliably driving and positioning a camera lens mount, however, are difficult to meet under the most ideal of conditions. It will be appreciated therefore, that the addition of new technology represented by the ranging and lens focusing system disclosed in the cited co-pending application to the camera structure disclosed in the afore-mentioned patents, involves a major manufacturing burden both in the fabrication and assembly of the mechanical components of the ranging system and in the adaptation of the system to existing camera components.